OPC DX Link Option for KEPServerEX

OPC DX

OPC Data eXchange (OPC-DX) provides for non-time critical horizontal transfers of data from a source server to a OPC-DX target server. The source server, which can be any OPC-DA or OPC-DX server, provides its source data through standard OPC-DA items, where as the target server contains the target item. OPC-DX defines the data transfer from the source item to a target item. This link between source and target is referred to as a DX connection. A DX connection is configured by OPC-DX clients using OPC-DX specific services. OPC-DX also defines related OPC-DA items that clients can use to control and monitor connections using OPC-DA interfaces. The OPC-DX architecture is illustrated below:



Configuration clients, such as our Data Exchange Client, use OPC-DA interfaces to browse DA/DX servers for source and target items. Target items are always resident in the DX server. Source items may be resident in DA or DX servers, including the target DX server. The configuration client selects the source and target items and uses them to define its DX connections. DX connections are defined in terms of attributes that identify the source and target items, characterize the data transfer between them, and provide additional descriptive information about the DX connection. The DX server stores its connections in a DX database. This database is accessible through the DX server address space. The DX server periodically persists its database for use when restarting.

Any DA client is able to browse the database in the DX server using standard DA browse interfaces. The DX server allows clients to define the browse structure for connections using the concept of a browse path. The browse path is the path used to reach the DX connection when browsing the database. Branches within the browse path represent logical groupings of DX connections. Clients are allowed to define more than one browse path for each connection, thus enabling connections to belong to more than one logical grouping. The DX database also contains a list of source servers. Source servers are any DA or DX server that contains source items. Each source server entry in the database specifies the address of the source server and the type of interface used by the DX server to access it (e.g. DA 2.05).

The OPC-DX specific services may be used concurrently by configuration clients to configure and maintain connection and source server definitions in the database. Clients may use these services to operate on source servers and connections. Connection and source server definitions are assigned a unique version with each modification, such that operations made on the same connection or source server by multiple clients can be handled appropriately. Connections and source servers become operational when they are added, independent of whether or not the client that created them remains connected to the DX server (i.e., the configuration client is not required by the runtime component of OPC-DX). They remain defined in the DX server until a client explicitly removes them. Connections and source servers have configurable default attributes that define whether or not data transfer is to be enabled when they become operational. When access to a source server is disabled, the DX server is not permitted to be connected to it. In this case, none of the DX Connections with source items contained by it may access data from it. Once a connection is configured and enabled for data transfer, the DX server accesses the source server to acquire the value of its source item. The DX server updates the target value after performing any necessary conversions, transformations, substitutions, or manual overrides.

For more information please refer to the OPC DX specification on the OPC Foundation website.

Features